*{
    box-sizing: border-box;
}
.app{
    width: 500px;
    height: 300px;
    padding-top: 50px;
    background-color: pink;
}
.node{
    width: 400px;
    height: 200px;
    padding-top: 50px;
    margin: 0 auto;
    background-color: plum;
}
.subnode{
    width: 300px;
    height: 100px;
    padding-top: 25px;
    margin: 0 auto;
    background-color: powderblue;
}
.child{
    width: 200px;
    height: 50px;
    margin:  0 auto;
    background-color: salmon;

}